The poor man's daily snapshot, glastree builds live backup trees, with
branches for each day. Users directly browse the past to recover older
documents or retrieve lost files. Hard links serve to compress out
unchanged files, while modified ones are copied verbatim. A prune
utility effects a constant, sliding window.

Satoru Takabayashi has written a similar program, in Ruby, pdumpfs.

Inspired by Plan9, of course.
